1. Field of the Invention
The present invention relates to a vertical cavity surface emitting laser (VCSEL) which has a laser light emitting region on the top face, particularly to a VCSEL which can be suitably applied to purposes necessitating light output in the low-order transverse mode.
2. Description of the Related Art
A VCSEL emits light in the direction perpendicular to the substrate unlike the existing edge-emitting laser diodes. In the VCSEL, many devices can be arranged in a state of a two dimensional array on the same substrate. Therefore, the VCSEL has recently attracted attention as a light source for a digital copy machine or a printer.
In the past, in the foregoing type of VCSEL, a pair of multilayer reflectors is formed over the semiconductor substrate, and an active layer becoming a light emitting region is provided between the pair of multilayer reflectors. In the region between one multilayer reflector and the active layer, in order to improve efficiency of current injection into the active layer and lower the threshold value current, a current confinement layer having a structure in which a current injection region is narrowed is provided. Further, an n-side electrode is provided on the bottom face side, and a p-side electrode is provided on the top face side. The p-side electrode is provided with a light emitting aperture to emit laser light. In the VCSEL, a current is confined by the current confinement layer, and then injected into the active layer where light is emitted. While the emitted light repeats reflection between the pair of multilayer reflectors, the light is emitted as laser light from the light emitting aperture of the p-side electrode.
It is known that in the foregoing VCSEL, while basic transverse mode oscillation is mainly generated in the central region in the laser light emitting region, high-order transverse mode oscillation is mainly generated in the outer edge region thereof. Therefore, there is a disadvantage that when the light emitting aperture is excessively widened to obtain high output of the VCSEL, laser light in the high-order transverse mode is also outputted at high output.
Therefore, to solve the foregoing disadvantage, many techniques for controlling transverse mode oscillation have been reported. For example, in Japanese Unexamined Patent Application Publication No. 2003-273459, a technique for providing a current confinement layer having a structure in which as the location of the current injection region becomes closer to the active layer, the diameter of the current injection region becomes larger has been disclosed.